Carding is one of the fundamental operations in manufacturing of yarn and in the production of carded nonwoven products. Carding is a process that transforms the raw material, such as cotton, wool or polyester fibres, into a coherent web by disentangling and straightening the fibres and eliminating undesired materials. At the output side of the card, the web is combined into a so-called “sliver”, a one dimensional ribbon of fibres; or transferred as a web to the next process. The control of fibres during the carding process is carried out through metallic and/or flexible card clothing and by control of the air flows. Although the basic principles underlying the carding process have not changed for over 100 years, there has been a constant improvement in the manufacturing technology thus resulting in an improved speed and efficiency.
U.S. Pat. Nos. 4,233,711, 4,964,195, 464,389, 5,755,012 and 6,408,487 relate to different metallic card clothing. WO00/26450 describes card clothing comprising a strip of profile wire having a plurality of longitudinally aligned teeth with respective overhanging tips. The edge-face of each tooth under the overhanging tip includes at least one undercut edge-segment spaced along the edge-face from the tip. This undercut edge-segment increases the retention of fibres by the edge-face during carding by means of a preferably substantially horizontal step in the undercut. WO00/26450 describes that for performance and lifetime related reasons, the undercut edge segments can be optimized by careful design, this statement, however, leaves the drawback unsolved that the wires cannot be made via state of the art rotary punching technology.
The prior art fails to address a desirable card clothing that has the following characteristics (i) a perfect control of the fibre, this is an extremely critical step during carding because the card clothing must not only be capable of penetrating into the fibre material, but also retain the fibre without resulting in damage to the fibres; (ii) desirable card clothing should be able to transfer the fibre between rollers clothed with wires, e.g. from the main cylinder to the removal cylinder known as doffer. An issue noted with the wire profile known in the art is that strong fibre taking capacity leads to fibre loading at the stop-start of the cards. It should be noted that the type of fibre also plays a major part in transfer for instance the card profile being used for woven or non-woven units. (iii) desirable card clothing should minimize the various macroscopic deformations to the fibres such as transverse compression, stretching and twisting; (iv) Certain wire profiles known in the art such as in WO 00/26450 cannot be produced by rotary punching technique and it is thus desirable that the card clothing be mass producible using rotary punching technique for specific geometries and; (v) must be wear resistant so that replacements of card clothing on the rollers and plates of the carding machines are less common thus saving time and maintenance costs. The wire profile known in the art have problems with decreased tooth strength due to stress concentration at the edges thus occurrence of breakage of part of tooth is common and the fibre retention capacity is lost.
In order to obtain desirable card clothing, major amount of research has been focussed on the geometry of the card clothing, these hook shaped card clothing act directly on the fibres to break down and tease the tufts into individual fibres; and to orient the fibres.
To manufacture card clothing, wire forms the basic starting material which is subjected to one or more drawing and rolling operations followed by punching a series of consecutive slots to form the teeth using a suitable mechanical stamping device as described in GB 2 257 164 A.
GB 2 257 164 A elaborates on two punching techniques, vertical and rotary, both these techniques are known for producing teeth in a blade. The vertical punching technique involves a vertically reciprocating cutter tool passing in and out of a shaped die over which the blade is temporarily held. Thus, in accordance with this known technique, the blade must be moved intermittently and periodically held stationary in order to perform the punching operation. One of the disadvantages with this technique is that it is a very slow process to manufacture saw toothed wire and it drastically impacts the efficiency of manufacturing rollers or replacing rollers, cylinders, doffers with saw toothed wires because the low volume output. The rotary punching technique on the other hand involves the use of a rotating cutting tool which is set to pass through a shaped die, over which the blade passes continuously. The advantage of this technique is the high speed and ability to manufacture saw toothed wires in kilometers of stretch in short span of time. U.S. Pat. No. 6,195,843 describes one rotating cutting tool which has a rotary milling spindle with a blanking tool attached to it, the angular position of the milling spindle can be continuously registered by means of an angular decoder, and the feed mechanism can be controlled on the basis of the angular position that has been determined in this manner. There is however a disadvantage with the rotary punching technique which is the limitation to manufacture any geometry and shapes of saw toothed wire. Furthermore GB 2 439 638 mentions the disadvantages of manufacturing card clothing using mechanical tool means (referring to vertical and rotary punching) and in particular mentions the problems of oxide residues during thermal treatment, production accuracy deteriorates with wear and tear on the tool and suggests to use laser for producing card clothing. Precision may be better since the laser beam doesn't wear during the process. A disadvantage of laser cutting is the high energy required. With part geometries, lasers also face the problem with a part absorbing more heat, and consequently the probability of thermal runaways or violent reactions like blowouts increases.